Method for treating water using an organic sanitizer and a persulfate

ABSTRACT

Persulfates are used to provide water clarity when organic sanitizers such as biguanides are utilized for sanitizing recreational waters. Persulfate applications of 2 ppm or more can be used. Additionally, maintenance applications of the persulfate or the bisulfate can be used.

This application is a continuation of application Ser. No. 08/051,488,filed Apr. 22, 1993, now abandoned.

FIELD OF THE INVENTION

The invention is in the field of water treatment. More particularly, itis in the field of providing clear and microbially safe recreationalwater.

BACKGROUND OF THE INVENTION

In maintaining water systems for recreational use a number of parametershave to be controlled. These factors include pH, alkalinity, and calciumconcentration. Generally, a pH of 7.2-7.8, alkalinity within the rangeof 85-170 ppm, and calcium or magnesium hardness within the range of 140to 250 ppm is desired for recreational waters.

In addition to the above it is important to provide clear andmicrobially safe water. Chlorine and other halogen based sanitizationsystems or products actually perform two tasks which are important tothe upkeep of swimming pool and bathing waters.

The first task, sanitization, involves the biocidal or microbiocidaltreatment of the pool water. Chlorine is a good sanitizer because it canpenetrate the cell wall of microbiological agents and then destroy them.

The second task, involves providing water clarity by oxidizing dissolvedor suspended matter in the water which can provide a nutrient source forpathogens. The unwanted matter include suntan oils, urea, leaves, soiland other matter introduced by the bathers or the wind.

Historically, chlorine has been successfully used as a treatment forboth sanitization and as a water clarity agent because it is both apowerful biocide and oxidizing agent. However, the use of chlorine hasfallen into disfavor because of environmental issues.

As an alternative to chlorine, quaternary ammonium compounds, such asthe biguanides, and particularly the polyhexamethylene biguanides havebecome widely used as sanitizers for swimming pool water and otherrecreational water. Although these organic compounds are goodmicrobiocides, they are not able to oxidize matter as required toprovide water clarity. A 27.5% hydrogen peroxide has been used for thatpurpose because, like chlorine, it has the ability to oxidize organiccompounds to forms which are more readily removed from the water.Hydrogen peroxide is also used because it is a powerful oxidizing agent.It is such a powerful oxidizing agent that this liquid can initiatecombustion and cause burns to skin and eyes. However, it is notsubstantially reactive with the biguanides, which are oxidizable organiccompounds.

In fact the biguanides are readily removed from pool water by oxidizingthem with Oxone® peroxygen, 2KHSO₅.K₂ SO₄.KHSO₄, which is commonly usedas an oxidizer to destroy biguanide in biguanide sanitized pools priorto instituting chlorine sanitization. Oxone provides about 4.5% activeoxygen for this purpose. The active ingredient in Oxone is potassiummonopersulfate, also known as potassium caroate, KHSO₅. Oxone is aregistered trademark of DuPont.

The persulfates have been used as oxidants for providing water clarityin conjunction with inorganic sanitizers such as chlorine, bromine, andchloro and bromo isocyanurates, but have not been used as an oxidantused in conjunction with organic sanitizers because of their similarityto the active ingredient of Oxone (potassium caroate), which is known tosubstantially oxidize organic sanitizers.

SUMMARY OF THE INVENTION

We have discovered that despite its chemical similarity to themonopersulfates, sodium persulfate, Na₂ S₂ O₈, can be substituted forhydrogen peroxide as an oxidizer suitable for restoring or maintainingclarity to recreational waters when organic sanitizers are used. Moreparticularly, persulfate can be used with and is substantiallynon-reactive with biguanides including polyhexamethylene biguanide.Thus, water can be treated with the simultaneous or sequential additionof a biguanide and a persulfate to sanitize and clarify the water. As anadditional benefit, such use of persulfate aids in the pH control of thewater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Swimming pool and other recreational water can be treated using asanitizer for biocidal control, and an oxidizer for converting dissolvedor suspended matter to removable forms. Where an organic sanitizer suchas biguanide is used, it is normally used at a dosage of 30 ppm or more,although concentrations within the range of from 20 to 60 ppm areacceptable. Persulfate is a suitable oxidizer which acts as a waterclarity agent. It can be applied to water at a rate of 1 to 30 ppm.However, an application of 2 to 9 ppm is generally preferred. In either,the effective amount of sanitizer or water clarity agent depends on thecondition of the water being treated, and can be less than or greaterthan the figures given. The most effective dosage or application can bedetermined empirically using tests available and known to those ofordinary skill in the art.

Ammonium, potassium, and sodium persulfate have been found to beeffective as oxidizers for water clarification when used alone or incombination, however, the sodium salt is preferred. These salts can beused alone or as part of a formulation. The amount of persulfate saltrequired depends on the amount of active oxygen that is needed forestablishing or maintaining swimming pool water clarity and is usuallydetermined empirically by the person maintaining the pool, since therequirements vary with the concentration and nature of the pollutantsbeing removed.

ClearAdvantage® peroxygen, a formulation containing sodium persulfate,plus inerts is suitable as a source of persulfate for use withbiguanide. ClearAdvantage is a trademark of FMC corporation.

As discussed above, sodium persulfate provides an acceptable level oftreatment; however, higher application rates may be appropriate for thefirst application followed by lower subsequent application rates. Thehigher initial rate may be needed for a pool in which treatment is justbeing instituted because high demands for oxidizer on startup is notunusual. As pool treatment progresses the demand generally is reducedand a steady state of organic contaminant and oxidizer consumption canbe approximated.

A maintenance concentration of persulfate within the range of from 2 to9 ppm are optimal, while concentrations of up to 30 ppm persulfateprovides a satisfactory water clarity and is suitable as a maintenancelevel of persulfate.

The persulfate dosage form can contain from 5% to 100% persulfate. Morepreferred are dosage forms which contain from 50 to 80% persulfate, andmost preferred are dosage forms which contain from 60 to 80% persulfate.A formulation containing 75% sodium or potassium persulfate and 25%inert ingredients provides sufficient active oxygen for oxidizing thematter in the pool.

The other ingredient(s) which may be included in the water clarifyingformulation can be a flow enhancer or stabilizer for the persulfate.Persulfate is best presented as a formulation containing adjuncts forimproved flowability, for anti-caking, and for pH adjustment. Inaddition, adjuncts such as sodium sulfate can be added which inhibit theautoignition of the persulfate, making it safer for storage andtransport.

The "other ingredients" may be comprised of a number of inorganic andorganic water soluble species, alone or in combination that arecompatible with persulfate salts to present a dry or substantially dryformulation.

The "other ingredients" can include the sodium, potassium, or ammoniumsulfates or bisulfates, as well as the other soluble or weakly solublesulfate or bisulfate salts. Also included are various forms ofcarbonate, bicarbonate, and sesquicarbonate. Sodium salts are preferredbut other salts, where available, are suitable.

In order to obtain satisfactory sanitization and water clarification thechemical balance of the water must be established. The primary factorswhich are addressed for this purpose are pH, alkalinity, and hardness.The pH is generally kept within the range of from 7.2 to 8.0. Alkalinityis generally kept within the range of from 80 to 130 ppm, and hardnessis generally kept within the range of from 150 to 250 ppm. Howeveroptimal values for are generally found within the range of from 7.2 to7.6, of from 100 to 120 ppm, and of from 160 to 200 ppm for pH,alkalinity, and hardness respectively. Not all of these factors must beadjusted in every water.

Suitable ingredients for adjusting pH include sodium hydroxide or sodiumcarbonate for increasing pH, and sodium bisulfate or hydrochloric acidfor decreasing pH. Other ingredients known to those skilled in the artof pool maintenance can also be used.

Suitable ingredients for adjusting alkalinity include sodiumbicarbonate, sodium sesquicarbonate and other alkalinity adjusters knownto those of ordinary skill in the art of pool maintenance.

Suitable ingredients for adjusting calcium or magnesium hardness includesoluble calcium or magnesium salts such as calcium chloride, magnesiumchloride, calcium carbonate, magnesium carbonate, and the like.

In addition to the above, ingredients can be added to the water forcontrolling other factors, such as color, algae growth, pool linerstaining, and foaming and other problems which are known in theindustry. Those factors can be controlled using chemicals and ortechniques known to those of ordinary skill in the art of poolmaintenance. These ingredients may include but are not limited topolymers, antifoams, algaecides, chelating agents, sequestering agents,and the like.

In addition to the above, chelating agents which tie up metal cationscan improve the efficacy of the treatment, since such cations cancatalyze oxidation reactions and lead to excessive use of oxidizingagent. Tetra sodium ethylenediaminetetraacetate hydrate, edta, and otheragents known to those of ordinary skill in the art can be used.

Moreover, antichlors, such as sodium thiosulfate can be used foreliminating chlorine from the water in a pool if the water supply tothat pool has been chlorinated.

The following examples further illustrate the invention without limitingthe scope thereof.

EXAMPLES 1-3 A Comparison of Oxidizing Agents

This study was conducted with four 70 gallon simulated pools maintainedper the methods described herein. Teel Water Filter Cartridges (Model1P753-A) and Little Giant pumps (Catalog No. 501003) were used torecirculate pool water every six hours.

Pool water was adjusted with sodium bicarbonate to achieve an alkalinityof 120 ppm and calcium chloride to achieve a calcium hardness of 160ppm. Each pool was preconditioned with Baqua Start™ reducing agent(sodium thiosulfate) and Baq Out™ chelating agent (tetra sodiumethylenediaminetetraacetate hydrate). Baqua Start™ eliminates residualchlorine from the tap water used to fill the pools. Baq Out™ is achelating agent for metals. Baquacil™biguanide was used in theexperiments below as the sanitizer. Bacquacil is primarily apolyhexamethylene biguanide. Bacquacil, Baq Out, and Baqua Start aretrademarks of ICI Americas.

Baquacil concentration, water turbidity, and pH were measured on a dailybasis. Calcium hardness, alkalinity, and total dissolved solids (TDS)were measured on a weekly basis. The sodium persulfate and hydrogenperoxide content of each pool were measured daily for the last fourweeks of the study.

Pool pH was determined with a Lovibond Photometer PC20. The PC20measures the absorbance of solutions treated with phenol red. Baquacilconcentrations were measured with the STC-F Colorimeter. The STC-Fmeasures the absorbance of solutions treated with the Baqua Test IIIindicator solution.

Turbidity was measured with a Lamotte Turbidity Meter (Model 2008). NTU,the units for turbidity, are an acronym for Nephelometric TurbidityUnit. Nephelometry is the measurement of light scattering in thedirection perpendicular to its propagation.

Calcium hardness and alkalinity were measured titrimetrically with aTaylor Technologies Test Kit. When required, chemical adjustments weremade according to the Taylor Technologies Water Chemistry Testing andTreatment Guide. Sodium persulfate and hydrogen peroxide were measuredcolorimetrically with a CHEMetrics, Inc. test kit (Model K-7870).

The four simulated pools were established according to the methodsoutlined in G. P. Fitzgerald and L. Faust, Bioassay for Algicidal vs.Algistatic Chemicals, Water and Sewerage Works, 110, 296-298, 1963, asdescribed above. Three simulated pools were maintained usingpolyhexamethylene biguanide as the sanitizer: and one pool was nottreated. One pool, the untreated pool, was used as the controlcorresponded to the use of no sanitizer with no oxidizer. Another poolcorresponded to the use of the sanitizer and no oxidizer. In a thirdpool sanitizer was used with a sodium persulfate water clarity agent. Ina fourth pool sanitizer was used with hydrogen peroxide as the waterclarity agent.

The data generated in Examples 1-3 are presented in Tables 1-3respectively.

Biguanide was initially added and maintained at 50 ppm. To simulate thewaste load from bathers a 1.5 ml dose of "bather load" was added to eachpool daily (table 2). In addition, a single 2 ml portion of castor oil,to simulate bather oils, was added to each pool prior to addition of theoxidizer.

Table 2 provides the application profile for sanitizer and/or for theoxidizer corresponding to the data points presented in Table 1. A 27.5weight percent hydrogen peroxide was used. To simulate bather load, amixture of inorganic and organic compounds and inorganic salts was addedfive times each week, as indicated in Table 2. A single addition ofcastor oil was made to each pool to simulate oils contributed bybathers.

Several data sets were collected. The efficacy of either oxidizer wasdetermined by measuring turbidity of the simulated pool water.Compatibility between sanitizer and oxidizer was determined throughmeasurement of the sanitizer content of each pool and measurement ofeither sodium persulfate or hydrogen peroxide levels. Samples fordetermination of total organics were collected on Day 1 and Day 28 andsubsequently analyzed.

During the course of the study, persulfate when used was applied to thesimulated pool four times at a one pound per 10K gallon of pool waterrate. The total application was equivalent to 36 ppm of sodiumpersulfate. For the pools in which hydrogen peroxide was used, thehydrogen peroxide was added once (Day 1) at a rate of one gallon per10,000 gallon of pool water. The total application was equivalent to 30ppm of hydrogen peroxide. Maintenance additions of sanitizer were madeon Day 13 and Day 28. Each addition was about 15 ppm.

The Table 1 data establishes that persulfate and sanitizer when usedtogether prevent the formation of turbid water and will provide apleasing appearance to pool water. Thus, the clarity of recreationwater, which is a major concern of pool owners, is provided for andmaintained.

Compatibility of the swimming pool oxidizer and the sanitizer areimportant for several reasons. Compatibility ensures that oxidizer andsanitizer are used efficiently. More importantly, if the two productsare compatible, the oxidizer will not catastrophically decompose thesanitizer and leave the pool water unprotected from bacteria introducedby normal pool use patterns. The Table 2 data establishes that eachoxidizer product had an effect on the sanitizer that was most pronouncedin the early portion of the treatment regimen. Subsequent additions ofpersulfate had little effect on the sanitizer. Clearly, neither 30 ppmof hydrogen peroxide nor 36 ppm sodium persulfate were detrimental tothe overall sanitization of the simulated pools.

These results support the claim that persulfate can effectivelyestablish and maintain pool clarity. It is noteworthy that the poolstreated with either persulfate or hydrogen peroxide behaved similarly,each requiring two "maintenance" additions of sanitizer (a total ofabout 30 ppm); while, the pool containing biguanide, which was notclarified with an oxidizer, required no additional maintenance additionsof sanitizer. This indicates that both hydrogen peroxide and persulfatedo oxidize the biguanide, albeit in very small quantities. Overall,sodium persulfate reacted with about 10 ppm more sanitizer than didhydrogen peroxide.

Moreover, Table 3, directed to total organic carbon analysis, shows thatsodium persulfate more effectively controlled the organic content of thepools, as determined by total organic carbon analyses, than did thehydrogen peroxide. In fact the data shows that with hydrogen peroxidethe total organic content of the pool would have increased by 20% whilea pool treated with sodium persulfate experienced a 24% decrease intotal organic carbon. Thus, total organic carbon can be decreased usingsodium persulfate depending on the system being treated. The decrease intotal organic carbon represents those carbon containing compositionsthat were removed from the system either by filtration or by theatmosphere.

                  TABLE 1    ______________________________________    Turbidity Results    Turbidity (NTU)          No Sanitizer                     Sanitizer  Sanitizer                                         Sanitizer    Day   No Oxidizer                     No Oxidizer                                Persulfate                                         H Peroxide    ______________________________________    1     0          0          0*       0#    2     0.06       0          0        0    5     0.35       0.2        0.02     0.06    6     0.21       0.1        0*       0    7     0.26       0.05       0        0    9     0.35       0.05       0        0    13    0.53       0.05       0        0    14    0.5        0          0        0    15    0.57       0          0*       0    17    0.59       0.05       0        0    19    0.66       0.03       0        0    20    0.65       0.05       0        0    21    0.7        0.09       0        0    23    0.8        0.12       0        0    26    0.58       0.1        0        0    28    0.6        0.13       0        0    29    0.63       0.15       0*       0    34    0.53       0.1        0.02     0    ______________________________________     #27.5% aqueous hydrogen peroxide added     *Sodium persulfate added

Example 2

                  TABLE 2    ______________________________________    Stability Results    Sanitizer Concentration (ppm)             Sanitizer    Sanitizer   Sanitizer    Day      No Oxidizer  Persulfate  H.sub.2 O.sub.2    ______________________________________    1        45           40*         45#    2        45           35          40    5        40           30          35    6        35           30*         35    7        40           30          35    9        55           28          36    13       53           22.sup.B    29.sup.B    14       53           34          40    15       50           43*         50    17       50           39          48    19       49           35          42    20       48           33          40    21       50           31          42    23       52           30          40    26       50           31          38    28       52           29.sup.B    35.sup.B    29       50           39*         45    34       48           29          41    ______________________________________     #Baqua Shock Added     *ClearAdvantage Added     .sup.B Maintenance Addition of Baquacil

Example 3

                  TABLE 3    ______________________________________    Total Organic Carbon Analyses    Percent TOC  Initial.sup.1                           Final.sup.2    Treatment    TOC (ppm) TOC (ppm)  % Increase    ______________________________________    Untreated    14        20         43.sup.3 >    Baq/No Oxidizer                 12        24.5       104    Baq/FMC Oxidizer                 17        13         -24    Baq/Baq Shock                 15        18         20    ______________________________________     .sup.1 Initial TOC = Total organic carbon     .sup.2 Final TOC = Total organic carbon     .sup.3 This may not be a true representation of TOC, because some organic     matter collected on the bottom of the tank.

EXAMPLES 4-8 Eight Week Study

Using the apparatus and general procedure described in Example 1, aneight week study was conducted to explore the use of organic sanitizerwith a persulfate. In this study four tables of data were collected,corresponding to data generated as and are presented as Tables 4-7corresponding to Examples 4-8. For each of these Examples, sufficientchemical was added to provide the concentration indicated. In a pool 30to 50 ppm of biguanide sanitizer was maintained to provide sufficientsanitizer for unexpected introduction of microorganisms.

In Table 4, an initial application of biguanide of approximately 50 ppmwas made to a simulated pool, and the biguanide concentration wasmonitored, with only one adjusting application of biguanide. Bisulfatewas added periodically to adjust pH, and at day 25, 1.855 grams ofbiguanide was added to prevent further falloff in biguanideconcentration. No adjustments were required for alkalinity, or hardness.The water clarity as expressed by turbidity was good, as were the flowrate.

In Table 5, the following initial applications were used: approximately50 ppm biguanide, and approximately 9 ppm sodium persulfate were added.Additional amounts of each were added to provide at least a thresholdlevel of the respective chemicals. Only two bisulfate additions wererequired for pH adjustment. Water clarity and flow rates through thefilter were good. No adjustments were required for alkalinity orhardness.

In Table 6, the following initial applications were used: 50 ppmbiguanide, and 9 ppm sodium persulfate.

In Table 7, the following intitial applications were used: 50 ppmbiguanide and 30 ppm hydrogen peroxide.

In Table 8, the following initial applications were used: 50 ppmbiguanide and 4.5 ppm sodium persulfate.

Example 9

Using the apparatus and procedure described in Example 1, a 24 hourstudy was conducted, to establish the ability of Oxone peroxygen tooxidize a biguanide. At an oxidant application rate of 6 ppm, 4.9 gramssanitizer/70 gallons of water was consumed in 24 hours. Extrapolated toa 60 day time period, this would amount to 300 grams. This example showsthat Oxone is too reactive with biguanide to be used in conjunction withbiguanide for sanitizing and clarifying water.

Table 9 below uses the data provided in tables 4-8 together with thedata from Example 9. This table illustrates that persulfate issubstantially more compatible with biguanide than Oxone and similarly ascompatible as hydrogen peroxide. The left hand column, labeled Tblprovides the Table number from which the data was taken.

                  TABLE 9    ______________________________________    Biguanide Consumption                        Oxidant      Biguanide(g)    Tbl     Oxidant     Application rate                                     (60 day)    ______________________________________    4       none        --           1.9    7       H.sub.2 O.sub.2 (27.5%)                        9.2 lbs/mo.  9.5    --      Oxone       1.0 lbs/24 hour                                     4.9.sup.1    8       Na.sub.2 S.sub.2 O.sub.8                        0.38/lb/Month                                     12.4    6       Na.sub.2 S.sub.2 O.sub.8                        0.75 lb/3 weeks                                     13.6    5       Na.sub.2 S.sub.2 O.sub.8                        0.75 lb/week 31.0    ______________________________________     .sup.1 This 24 hour test corresponds to a 300 gram consumption of     biguanide when extrapolated to 60 days.

Example 10

In Table 10 below the relative oxidant efficiency of hydrogen peroxideand sodium persulfate is presented at different application rates. ClearAdvantage®peroxygen, containing 0.75 weight percent sodium persulfatewas used for some of the studies. Clear Advantage is a registeredtrademark of the FMC corporation. A 27.5% aqueous hydrogen peroxide wasused for the studies presented herein.

Table 10 illustrates that persulfate is much more efficient in its useof active oxygen than hydrogen peroxide. The data used herein is derivedfrom tables 5-8. The column marked "Table" indicates the Table fromwhich the data was taken.

                  TABLE 10    ______________________________________    Oxidant Efficiency                Dosage   Oxidant   Oxidant    Oxidant     lb/mo    AO %      AO(lb) Table    ______________________________________    H.sub.2 O.sub.2 (27.5%)                9.2      13        1.20   7    ClearAdvantage                4        5         0.20   5    Clear Advantage                0.5      5         0.025  8    Na.sub.2 S.sub.2 O.sub.8                3        6.6       0.20   5    Na.sub.2 S.sub.2 O.sub.8                0.375    6.6       0.025  8    ______________________________________

Example 11

The information used in Table 11 below, is based on the data found inTables 4-7. Table 11 illustrates that pH adjustment requirements arelowest when sodium persulfate is used. Thus the use of persulfate as thewater clarity agent can reduce the use of pH control chemicals. Thecolumn marked "Tbl" indicates the Table from which the data was taken.

                  TABLE 11    ______________________________________    pH Control with Bisulfate                                      Oxidant          NaHSO.sub.4                   Average            Application    TBL   (g).sup.1                   pH.sup.2  Oxidant  Rate    ______________________________________    4     18.7     7.71      none     --    7     26.2     7.73      H.sub.2 O.sub.2 (27.5%)                                      9.2 lb/mo    5     9.92     7.66      Na.sub.2 S.sub.2 O.sub.8                                      0.75 lb/week    6     9.92     7.73      Na.sub.2 S.sub.2 O.sub.8                                      0.75 lb/3 weeks    ______________________________________     .sup.1 Sodium Bisulfate use is over a 60 day time frame     .sup.2 Average pH is an average of pH measurement of the 60 day time     frame.     41 measurements were averaged.

Example 12

Evaluation of Flow Rate

The information provided in Table 12 below is based on the data found inTables 4-8. Table 12 illustrates that flow rates are consistently betterwhen persulfate is used than when hydrogen peroxide is used. Although itis not certain why this phenomenon occurs it is important because eithertoo much oxidation or too little oxidation can result in pool cloudinesswhich is undesirable. Perhaps this is due to the unique oxidizingcapability of the persulfate. Thus, the mere fact that flow rates areimproved when using persulfate, does not by itself establish efficacy asa water clarity agent. For that, it is also important to actuallyprovide acceptable water clarity. The column marked "Tbl" indicates thetable from which the data was taken.

                  TABLE 12    ______________________________________                             Flow              (f.sub.ai -    Tbl. Oxidant  Oxidant    Adjust                                   Avg f.sub.i                                         Avg f.sub.ai                                               f.sub.i)    ______________________________________    4    None     --         8     668   898   230    7    H.sub.2 O.sub.2                  9.2 lb/mo  19    470   833   363    5    Na.sub.2 S.sub.2 O.sub.8                  0.75 lb/wk 16    559   867   308    6    Na.sub.2 S.sub.2 O.sub.8                  0.75 lb/3 wk                             8     700   904   204    ______________________________________     Note: 27.5% hydrogen peroxide was used.

    TABLE 4      Biguanide - Sodium Persulfate Compatibility Study Biguanide Only     Biguanide.sup.1 Sodium Persulfate H.sub.2 O.sub.2 (27.5%)  Bisulfate     Alkalinity.sup.1 Turbidity Calcium.sup.1 TOC TDS.sup.1 Flow.sup.+1 Day     Date (ppm) Addition (grams) (ppm S.sub.2 O.sub.8) Addition (grams) (ppm     H.sub.2 O.sub.2) Addition (mL) pH.sup.1 Addition (grams) (ppm) (NTU)     (ppm) (ppm C) (ppm) (mL/min)       1 12/15 48   7.80  110 -0.04 220 9.5 520 830  12/15 1 (1 HR) 50   7.76     2 12/16 48   7.87 3 12/17 48   7.90  110 -0.02    845 4 12/18 48   >8.00     8.0  -0.01 7 12/21 48   7.43   -0.01    745 8 12/22 48   7.62  100 9     12/23 46   7.63   -0.06    (720) 890 14 12/28 45   7.74  100     800 15     12/29 44   >8.00 3.56  -0.03 16 12/30 42   7.59  90     (770) 965  1993     22* 1/5 45   7.77  90 9.8 900 23 1/6 42   7.79   -0.01 210   (575) 875     24 1/7 43   7.74  90 25 1/8 43 1.855  7.62   -0.02    850 28 1/11 46     7.51  90    560 790 29 1/12 46   7.65   -0.02 30 1/13 45   7.63 31 1/14     46   7.73  90     (755) 950 32 1/15 46   7.90 3.56  -0.03   560 35 1/18     47   7.52  95     820 36 1/19 46   7.63   -0.01  9.8 560 37 1/20 44     7.59 38 1/21 46   7.65  90 39 1/22 42   7.70   -0.01    (700) 990 42     1/25 46   7.64  90    570 965 43 1/26 46   7.90   -0.04 200 44 1/27 44     7.58 45 1/28 43   7.66      570 46 1/29 45   7.58  90     880 49 2/1 42      7.63  90    560 810 50* 2/2 42   7.67   -0.04  6.5  (370) 800 51 2/3 45       7.87 52 2/4 41   7.54 53 2/5 42   7.59  90    560 (730) 880 56 2/8 43      7.90  90    560 840 57 2/9 41   7.97 3.56   220 58 2/10 40   7.66 59     2/11 43   7.59  90 -0.03    820 60 2/12 42   7.60 64* 2/16 41   7.78  90        540 (720) 830     *tank stirred     .sup.+ flow numbers in parenthesis represent initial, uncorrected flow     rate on day of test     .sup.1 ideal range: Biguanide  30-50 ppm, pH  7.2-8.0, Alkalinity  100-15     ppm, Calcium  175-250 ppm, TDS  <1000, Flow  740-1000 mL/min     .sup.2 maximum pH reading on Lovibond PC 20 Photometer is 8.0     Biguanide added as a 20% solution     Experiment conducted in 70 gallon simulated pool

    TABLE 5      Biguanide - Sodium Persulfate Compatibility Study Biguanide with Sodium     Persulfate @ 0.75 lb/10K gal/week Biguanide.sup.1 Sodium Persulfate     H.sub.2      O.sub.2 (27.5%)  Bisulfate Alkalinity.sup.1 Turbidity Calcium.sup.1 TOC T     DS.sup.1 Flow.sup.+1 Day Date (ppm) Addition (grams) (ppm S.sub.2     O.sub.8) Addition (grams) (ppm H.sub.2 O.sub.2) Addition (mL) pH.sup.1     Addition (grams) (ppm) (NTU) (ppm) (ppm C) (ppm) (mL/min)       1 12/15 48   2.38  7.46  100 0.01 200 7.6 520 840  12/15 1 (1 HR) 44     >7   7.65 2 12/16 46  7   7.53 3 12/17 44  7   7.51  100 -0.01    (170)     800 4 12/18 39  7   7.73   -0.03 7 12/21 36 3.18 5.6   7.77   -0.02     (450) 880 8 12/22 41  4.2 2.38  7.55  100 9 12/23 37  >14   7.74   -0.11        (625) 890 14 12/28 32  <14   7.74  100     (480) 890 15 12/29 29 4.6     <14 2.38  8.00 3.56  -0.03 16 12/30 36  <21   7.43  95     (600) 865     1993 22* 1/5 32  >14 2.38  7.64  90   12.2 (510) 840 23 1/6 30  <28     7.55   -0.04 210   (470) 850 24 1/7 31  >21   7.64  95 25 1/8 29 5.565     <28   7.7   -0.01    (640) 840 28 1/11 32  21   7.54  100   610 (610)     785 29 1/12 32  21 2.38  7.7   -0.01 30 1/13 32  >28   7.54 31 1/14 31     28   7.62  90     (670) 930 32 1/15 28 5.83 28   7.73   -0.01   600 35     1/18 33  28   7.66  90     780 36 1/19 32  >28 discontinued  7.87     -0.01  11.0 600 37 1/20 31  28   7.50 38 1/21 30  28   7.71  90 39 1/22     32  28   7.72   -0.03    (680) 920 42 1/25 30  28   7.79  90    600 830     43 1/26 27 6.625 28   7.61   -0.05 210 44 1/27 38  28   7.66 45 1/28 36     21   8.00 6.36     610 46 1/29 34  21   7.29  80     760 49 2/1 29 6.625     21   7.49  80    600 (710) 910 50* 2/2 38  21   7.50   -0.07  8.8  (340)     870 51 2/3 39  21   7.60 52 2/4 40  21   7.56 53 2/5 39  21   7.49  80      610 760 56 2/8 37  21   7.81  80    610 (750) 820 57 2/9 37  21   7.72        220 58 2/10 34  21   7.71 59 2111 36  21   7.71  80 -0.02    (680)     900 60 2/12 36  21   7.73 64* 2/16 34  14   7.88  80    580 (560)     *tank stirred     .sup.+ flow numbers in parenthesis represent initial, uncorrected flow     rate on day of test     .sup.1 ideal range: Biguanide  30-50 ppm, pH  7.2-8.0, Alkalinity  100-15     ppm, Calcium  175-250 ppm, TDS  <1000, Flow  740-1000 mL/min     .sup.2 maximum pH reading on Lovibond PC 20 Photometer is 8.0     Biguanide added as a 20% solution     Experiment conducted in 70 gallon simulated pool

    TABLE 6      Biguanide - Sodium Persulfate Compatibility Study Biguanide with Sodium     Persulfate @ 0.75 lb/10K gal/3 weeks Biguanide.sup.1 Sodium Persulfate     H.sub.2      O.sub.2 (27.5%)  Bisulfate Alkalinity.sup.1 Turbidity Calcium.sup.1 TOC T     DS.sup.1 Flow.sup.+1 Day Date (ppm) Addition (grams) (ppm S.sub.2     O.sub.8) Addition (grams) (ppm H.sub.2 O.sub.2) Addition (mL) pH.sup.1     Addition (grams) (ppm) (NTU) (ppm) (ppm C) (ppm) (mL/min)       1 12/15 51   2.38  7.69  100 -0.03 210 7.2 460 780  12/15 1 (1 HR) 51     7   7.87 2 12/16 46  7   7.76 3 12/17 41  7   7.74  110 -0.02    (740)     810 4 12/18 41  7   7.74   -0.01 7 12/21 38 3.18 5.6   7.80   -0.03     800 8 12/22 41  4.2   7.66  100 9 12/23 40  4.2   7.72   -0.03    790 14     12/28 37  2.8   7.80  100     (700) 875 15 12/29 36 4.6 2.8   >8.00 3.56      -0.05 16 12/30 42  2.8   7.58  90     (690) 900  1993 22* 1/5 42  2.1     2.38  7.82  90   10.1  870 23 1/6 40  14   7.60   -0.02 220   (610) 905     24 1/7 38  <14   7.72  90 25 1/8 40 2.65 14   7.84   -0.01    915 28     1/11 37  >7   7.72  90    550 790 29 1/12 39  >7   7.66   0.0 30 1/13 39      >7   7.71 31 1/14 39  >7   7.79  90     795 32 1/15 38 3.18 >7   7.71     - 0.03   530 35 1/18 39  7   7.92  90     (750) 990 36 1/19 40  <7     7.73   -0.02  11.7 540 37 1/20 39  >5.6   7.77 38 1/21 38  <5.6   7.76     90 39 1/22 39  5.6   7.76   -0.02    900 42 1/25 38  5.6   7.71  90     540 895 43 1/26 35  5.6 discontinued  7.82   -0.05 220 44 1/27 36  5.6     7.98 6.36 45 1/28 36  4.2   7.40      560 46 1/29 35  5.6   7.40  80     830 49 2/1 36  5.6   7.54  80    540 (670) 915 50* 2/2 37  5.6   7.60     -0.04  7.7  850 51 2/3 38  5.6   7.52 52 2/4 35  4.2   7.46 53 2/5 37     4.2   7.49  80    550 (690) 940 56 2/8 33  4.2   7.92  80    550 880 57     2/9 36  4.2 1.19  7.85    210 58 2/10 34  >7   7.76 59 2/11 35  >7     7.87  80 -0.02    860 60 2/12 34  >7   7.90 64 2/16 32  >7   7.92  80     530 (755) 900     *tank stirred     .sup.+ flow numbers in parenthesis represent initial, uncorrected flow     rate on day of test     .sup.1 ideal range: Biguanide  30-50 ppm, pH  7.2-8.0, Alkalinity  100-15     ppm, Calcium  175-250 ppm, TDS  <1000, Flow  740-1000 mL/min     .sup.2 maximum pH reading on Lovibond PC 20 Photometer is 8.0     Biguanide added as a 20% solution     Experiment conducted in 70 gallon simulated pool

    TABLE 7      Biguanide - Sodium Persulfate Compatibility Study Biguanide with 27.5%     H.sub.2 O.sub.2 @ 1 gal/10K gal/mo Biguanide.sup.1 Sodium Persulfate     H.sub.2      O.sub.2 (27.5%)  Bisulfate Alkalinity.sup.1 Turbidity Calcium.sup.1 TOC T     DS.sup.1 Flow.sup.+1 Day Date (ppm) Addition (grams) (ppm S.sub.2     O.sub.8) Addition (grams) (ppm H.sub.2 O.sub.2) Addition (mL) pH.sup.1     Addition (grams) (ppm) (NTU) (ppm) (ppm C) (ppm) (mL/min)       1 12/15 48    26.5 7.87  120 -0.04 190 9.1 510 775  12/15 1 (1 HR) 48      >30  7.84 2 12/16 48   30  7.80 3 12/17 43   30  7.74  125 0.08     (300) 845 4 12/18 42   30  7.84   -0.01 7 12/21 39 3.18  25  7.98 6.36     - 0.02    (210) 860 8 12/22 46   25  7.49  110     9 12/23 46   25  7.70       -0.08    (600) 910 14 12/28 41   20  7.84  110     (330) 835 15 12/29     38   20  >8.00 6.36  -0.08 16 12/30 41   20  7.63  100     (710) 890     1993 22* 1/5 40   15  7.80  110   11.9  (270) 815 23 1/6 37   15  7.91     -0.02 190   (400) 640 24 1/7 37   15  7.74  110 25 1/8 37 3.445  15     7.87   -0.02    (660) 840 28 1/11 42   12.5  7.80  110    580 (680) 980     29 1/12 42   10 26.5 7.76   0.0 30 1/13 41   50  7.52 31 1/14 40   45     7.95  100     (580) 965 32 1/15 39 2.92  40  7.82 3.56  -0.04   560 35     1/18 43   30  7.66  90     (540) 960 36 1/19 40   30  7.55   -0.00  11.0     560 37 1/20 40   25  7.59 38 1/21 44   25  7.70  95 39 1/22 39   25     7.58   -0.03    (660) 820 42 1/25 40   17.5  7.84  95    570 (600) 950     43 1/26 40   17.5  7.65   -0.05 200 44 1/27 38   17.5  8.00 6.36 45 1/28     39   15  7.38      590 46 1/29 40   15  7.35  90     (760) 830 49 2/1 38       12.5  7.63  90    570 800 50* 2/2 38   12.5  7.67   -0.03  7.0  (270)     965 51 2/3 38   10  7.62 52 2/4 38   10  7.67 53 2/5 39   10  7.56  90      580 (515) 855 56 2/8 37   7.5  7.91  85    570 (460) 950 57 2/9 39   5     26.5 7.97 3.56   210 58 2/10 37   35  7.61 59 2/11 36   35  7.65  90     -0.04    (330) 840 60 2/12 36   35  7.73 64* 2/16 36   35  7.80  90     560 (50) 830     *tank stirred     .sup.+ flow numbers in parenthesis represent initial, uncorrected flow     rate on day of test     .sup.1 ideal range: Biguanide  30-50 ppm, pH  7.2-8.0, Alkalinity  100-15     ppm, Calcium  175-250 ppm, TDS  <1000, Flow  740-1000 mL/min     .sup.2 maximum pH reading on Lovibond PC 20 Photometer is 8.0     Biguanide added as a 20% solution     Experiment conducted in 70 gallon simulated pool

    TABLE 8      Biguanide - Sodium Persulfate Compatibility Study Biguanide with Sodium     Persulfate @ 0.38 lb/10,000 gallons every 4 weeks Biguanide.sup.1 Sodium     Persulfate H.sub.2 O.sub.2 (27.5%)  Bisulfate Alkalinity.sup.1 Turbidity C     alcium.sup.1 TOC TDS.sup.1 Flow.sup.+1 Day Date (ppm) Addition (grams)     (ppm S.sub.2 O.sub.8) Addition (grams) (ppm H.sub.2 O.sub.2) Addition     (mL) pH.sup.1 Addition (grams) (ppm) (NTU) (ppm) (ppm C) (ppm) (mL/min)       1 2/12 34  >7   7.90        5* 2/16 32  >7   7.92  80   9.0 530 (755)     900 6 2/17 32  7   7.83 7 2/18 32  7   7.82   -0.02 8 2/19 33  7   7.92     80    530 960 11 2/22 33  7   7.85       910 12 2/23 32  <7   7.79  80     13 2/24 32  7   7.87    200 14 2/25 31  7   7.90     530 15 2/26 32  7     7.79  80 -0.02    880 17 3/1 32  <7   7.74       890 18 3/2 29 12.37 7     7.80  80    540 19* 3/3 47  <7   7.85   -0.01  13.9  880 20 3/4 48  5.6      7.82       820 23 3/8 44  5.6   7.87  70     815 24 3/9 44  4.2 1.59     7.91      540 25 3/10 45  >7   7.87    220  550 26 3/11 40  >7   7.92     -0.08 27 3/12 41  >7   7.90  70     810 31 3/16 39  7   7.87 32 3/17 43     7   <8.00 3.56 70 33 3/18 39  7   7.56      560 34 3/19 39  7   7.58       810 37 3/22 38  >7   7.80 6.36 60/160.sup.3    560 (710) 960 38* 3/23     40  7   7.70  140   17.0 39 3/24 42  7   7.97      650 (700) 860 40 3/25     40  >7   <8.00 3.56  -0.04 41 3/26 42  >7   7.66  140     880 44 3/29 41      7   7.95  150     870 45* 3/30 40  <5.6   <8.00 6.36   240 20.8 46 3/31     38  5.6   7.58  125     (580) 870 51 14/5 39  >5.6   <8.00 6.36 135     910 52* 4/6 40  5.6 1.59  7.63  120   18.5  870 53 4/7 36  >14   7.73     +0.04 54 4/8 37  <7   7.74  120    690 850 55 4/9 38  <7   7.74 58 4/12     36  <7   7.98 6.36 130     840 59* 4/13 35  <7   7.52  110     (510) 920     60 4/14 35  <7   7.65      690     *tank stirred     .sup.+ flow numbers in parenthesis represent initial, uncorrected flow     rate on day of test     .sup.1 ideal range: Biguanide  30-50 ppm, pH  7.2-8.0, Alkalinity  100-15     ppm, Calcium  175-250 ppm, TDS  <1000, Flow  740-1000 mL/min     .sup.2 maximum pH reading on Lovibond PC 20 Photometer is 8.0     Biguanide added as a 20% solution     Experiment conducted in 70 gallon simulated pool

We claim:
 1. A method of treating water, comprisingintroducing achelating agent to the water for the purpose of chelating metal cationspresent in the water; providing an antichlor; adding an effective amountof biguanide sanitizer; applying an effective amount of a saltcontaining S₂ O₈ oxidizer.
 2. The method of claim 1, wherein theeffective amount of sanitizer is within the range of 20 to 60 ppm,andwherein at least 2 ppm of a salt containing S₂ O₈ is applied to thepool water.
 3. A method of treating a recreational water, comprisingadding to the water 20 to 60 ppm of a biguanide as a sanitizer, at least2 ppm of an S₂ O₈ salt to clarify and to reduce the total organiccontent of the water, and then adding maintenance dosages of the S₂ O₈salt to the pool water at intervals spaced apart for maintaining atleast a threshold level of the salt in the water sufficient to maintainwater clarity.
 4. The method of claim 3, wherein the maintained level ofthe salt is within the range of 2 to 9 ppm, and the interval is withinthe range of from one week to two months.
 5. The method of claim 3wherein maintenance dosages of the S₂ O₈ salt are added at one weekintervals.
 6. A method of treating water, comprising introducing achelating agent to the water for the purpose of chelating metal cationspresent in the water; providing an antichlor; adding an effective amountof biguanide sanitizer; applying an effective amount of a S₂ O₈ salt toobtain at least a level of the salt in the water sufficient to obtainwater clarity, and then adding maintenance dosages of the S₂ O₈ salt tothe pool water at intervals spaced apart for maintaining at least athreshold level of the salt in the water sufficient to maintain waterclarity.
 7. The method of claim 6, wherein the effective amount ofsanitizer is within the range of 20 to 60 ppm, at least two ppm of theS₂ O₈ salt is added to the water, not as an algaecide, but to obtainwater clarity, and the maintenance dosages of the salt are added atintervals within the range of from one week to two months.
 8. The methodof claim 7, wherein the maintenance dosages of the salt are added at oneweek intervals.